The primary objective of this proposal is to evaluate the biochemical changes in cardiovascular tissues of spontaneously hypertensive rat (SHR) which could alter the intracellular Ca2 ion levels and thus provide the basis for increased vascular resistance and responsiveness seen in this model. The availability of Ca2 ion in the vascular smooth muscle cell will be investigated at two levels: 1. the factors which may influence the movement of Ca2 ion across the plasma membrane and 2. the mechanisms modulating sequestration and release of Ca2 ion by microsomes. In conjunction with the Na-Ca2 ion exchange across plasma membrane (Na ion-K ion)-ATPase would be a critical determinant of intracellular Ca2 ion. Our objectives include a detailed investigation of activity and kinetic properties of this enzyme in the cardiovascular tissues of SHR and WKY. Changes in the transition temperature(s) will be determined which could reflect alterations in the lipid composition of the membranes. Lipid composition will also be examined from cardiac and vascular smooth muscle membranes by TLC and GLC. The influence of phospholipids on (Na ion-K ion)-ATPase activity will be investigated through reconstitution studies employing partially purified enzyme into liposomes of known phopholipid composition and measuring the enzyme activity. Phosphorylation of the endogenous acceptor protein by the cyclic AMP-dependent protein kinase influences Ca2 ion seqestration by microsomes. To understand the molecular mechanisms which could result in reduced microsomal phosphorylation and Ca2 ion sequestration by microsomes isolated from cardiovascular tissues of SHR, experiments have been designed to evaluate the differences in cardiovascular tissues of SHR and WKY in: a. characteristics of endogenous phosphate acceptor protein, b. the activity and properties of cyclic AMP-dependent protein kinase isoenzymes and their ability to phosphorylate the endogenous membrane substrate, c. the activity of phosphoprotein phosphatase, and d. the activity of protein kinase inhibitor.